1. Field of the Invention
This invention relates to spark plugs having enhanced spark propagation and extended life. More particularly, it relates to a top and side firing plug having a center and a ground electrode with multiple edge surfaces.
2. Description of the Prior Art
The sole purpose of a spark plug is to produce a spark when needed to ignite a combustive fuel and air mixture within an internal combustion engine. A high voltage is applied to a center electrode, and a spark is created when the voltage discharges to ground by jumping across a narrow gap between the center electrode and a ground electrode.
Each discharge at least slightly fouls the spot on the ground electrode where the spark strikes it. A fouled spot has more resistance to a discharge than an unfouled spot so subsequent sparks will follow a path of least resistance to the ground electrode and thus avoid the fouled spots. Over an extended period of time, however, the entire ground electrode will become fouled and the discharges of sparks will be impeded; eventually the plug will fail and require replacement.
Spark discharge also wears down the center electrode as well; it becomes physically shorter with the passage of time. Conventional ground electrodes thus become less and less effective as the center electrode wears down because the distance the spark must jump increases as the center electrode shortens.
One way to extend the useful lifetime of a spark plug is to increase the surface area of the ground electrode. One example of a ground electrode having an increased surface area is disclosed in U.S. Pat. No. 5,280,214 to Johnson. The ground electrode takes the form of an annular ring disposed in surrounding relation to the center electrode. The surface area of the inner face of the annular ring is substantially greater than the surface area of a conventional ground electrode; accordingly, fouling of the plug takes longer and the effective lifetime of the plug is thereby extended. No means are provided, however, that take into consideration the shortening of the center electrode over time, and no means are suggested as to how the surface area of the ground electrode could be increased even further.
This invention includes several embodiments, all of them characterized by a ground electrode disposed coplanar with the free end of a center electrode so that sparks may propagate from the top and sides of the center electrode to the ground electrode. Both electrodes may be threaded or otherwise provided with surfaces that provide sharp edges that promote or facilitate spark propagation. As the center electrode decomposes, sparks continue to propagate therefrom because additional edges of the ground electrode become available to attract sparks.
In one embodiment, a plurality of circumferentially spaced apart flutes are formed in an annular ground electrode; each flute has an axis of symmetry parallel to the axis of the center electrode. The flutes provide numerous spark-attracting edges about the circumference of the ground electrode, thereby greatly increasing the number of spark-attracting edges and thereby substantially extending the effective lifetime of the plug.
In another embodiment, a square-edged groove is formed in the annular ground electrode in circumscribing relation thereto, i.e., normal to the flutes. A third embodiment eliminates the flutes and includes only the square-edged groove. Still further embodiments include beveled surfaces, knurled surfaces, sawteeth, screw threads, concentric rings, and the like formed in the ground electrode.
The purpose of the flutes, grooves, bevels, knurls, and other surfaces cut into the ground electrode is to provide a large plurality of sharp edges in the ground electrode. It has been found that such sharp edges provide a good path to ground for sparks. Since each edge will eventually become fouled, the large plurality of edges extends the lifetime of the plug.
Still another embodiment mounts the annular ground electrode within a slotted housing. The slots admit air into the housing and hence into the vicinity of the center electrode. In a preferred embodiment, the slots are partial helixes so that a swirling motion is imparted to air flowing through them. Such air flow further enhances the effectiveness of the spark generated by the plug.
The primary object of the invention is to provide a spark plug having an extended lifetime.
A more specific object is to advance the art of sparkplugs having annular ground electrodes by providing such electrodes with a large plurality of sharp edges to further enhance their effectiveness.
Still another object is to provide a means for creating a combustion-enhancing air flow in the vicinity of the spark.
Still another object is to provide a center electrode that continues operating even as it is shortened with wear.
Still another object is to provide a center electrode that continues operating even as it is shortened with wear.
These and other important objects, features, and advantages of the invention will become apparent as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.